1. Field of the Invention
The present invention relates to a fluorescent display device, and more particularly to a fluorescent display device which has a plurality of pattern display sections each composed of a plurality of fluorescent anodes, and which can arrange the pattern display sections at close intervals and, in addition, can give a high-quality fluorescent display with no display defects.
2. Description of the Prior Art
Fluorescent display devices, which feature good color of fluorescence, low-voltage drive, small power consumption, etc., have been frequently used as the display devices of various electronic apparatuses and the like.
With the increase or diversification of the information content to be processed by the electronic equipment or the like, it has become a general practice for the fluorescent display device to adopt a so-called multi-digit display mechanism in which a plurality of pattern display sections are provided on a substrate side by side and, in addition, to be adapted to display characters, numerals, figures, and the like.
In order to drive the above-mentioned so-called multi-digit pattern display sections, usually adopted is the dynamic drive system which can function with only a small number of outside-leading or external terminals and also with a small number of drive circuits.
For instance, the fluorescent display device which displays characters and the like by the use of dot matrices as shown in FIG. 1 is constructed and operated as follows:
Each of pattern display sections 1 (1a, 1b, 1c, . . . ) is composed of a plurality of dot-shaped anodes 2 each coated with fluorescent material. The anodes 2 are electrically connected by wiring conductors (not shown) so that those provided at the corresponding positions of the respective pattern display sections 1(1a, 1b, 1c, . . . ) are connected in common. The groups of corresponding anodes 2 thus connected are also connected to external terminals (not shown), respectively. Mesh-like control electrodes 3(3a, 3b, 3c, . . . ) (hereinafter referred to as grids) electrically independent of one another are provided above and opposite to the pattern display sections 1(1a, 1b, 1c, . . . ), being connected to external terminals (not shown), respectively. One or a plurality of filamentary cathodes 4, or filaments, which emit thermions when heated, are provided above and across the grids 3. The above-mentioned pattern display sections 1, grids 3 and filaments 4 are fixedly contained in a high-vacuum container (not shown), or package, so that the above-mentioned external terminals airtightly pass through the wall of the package. In operation, the anodes 2 are selectively given an anode voltage, while the grids 3 are given a grid voltage successively in a time-sharing manner. Among the anodes 2 of the pattern display sections, those thus selected are bombarded with electrons or thermions emitted from the filament or filaments 4, and thereby emit light for display.
FIG. 2 shows another example of the fluorescent display device, which is constructed and operated as follows:
Each of pattern display sections 11 (11a, 11b, 11c, . . . ) is composed of a plurality of anodes 2 coated with fluorescent material and arranged in a file or column. The pattern display sections 11 are equally spaced. In addition, the anodes 2 are electrically connected so that those disposed at the corresponding positions of the respective pattern display sections 11, or on the same row thereof, are connected in common. The groups of the anodes 2 thus connected are in turn connected to external terminals, respectively. Grids 13(13a, 13b, 13c, . . . ) electrically independent of one another are provided above the pattern display sections 11 (11a, 11b, 11c, . . . ), respectively.
In operation, the grids 13(13a, 13b, 13c, . . . ) are successively scanned, for instance, from left to right in FIG. 2, while the anodes 2 are given an anode voltage in synchronization with the above-mentioned scanning. Thus, fluorescent display can be performed.
In this example, as mentioned above, the pattern display sections 11(11a, 11b, 11c, . . . ) are equally spaced, and each of them consists of a plurality of anodes 2 arranged in a file or column. Therefore, it becomes possible to display characters and the like while moving them, for instance, from left to right in FIG. 2, or to dynamically display graphic symbols and the like.
In the above-mentioned examples, the fluorescent display device has grids 3 or 13 provided between the pattern display sections 1 or 11 and the filaments 4, one for each display section; the grids 3 or 13 are scanned in a time-sharing manner thereby making the pattern display sections 1 or 11 fluoresce for display. The fluorescent display device of this type has an advantage in that it can reduce the number of external terminals and that of drive circuits. However, it has such a disadvantage that display imperfections tend to occur on the anodes 2 positioned in the vicinity of the gaps between the grids 3 or 13. It is considered that these display imperfections are attributable to the following reasons:
FIG. 3 shows schematically how the above-mentioned conventional fluorescent display device works. When a pattern display section 1b provided on a substrate 5 is to be scanned, a grid 3a positioned at the left side of FIG. 3 is given a potential equal to that (zero) of the filaments 4 or lower (negative), while a grid 3b positioned at the right side of FIG. 3 is given a positive potential. In this case, the potential distribution in the vicinity of the filaments 4 and the gap "g" existing between the grids 3a and 3b may be shown by broken lines in FIG. 3.
Accordingly, electrons "e" passing through the meshy portion of the grid 3b and moving toward the anodes 2 of the pattern display section 1b are urged rightward by the action of an electric field formed by the negative potential given to the grid 3a. As a result, on the anodes 2 positioned in the vicinity of the gap "g" between the grids 3a and 3b, there appear regions where electrons "e" are not or insufficiently supplied. The regions on which no electron impinge become, for instance, display-defect regions S as shown in FIG. 1 thereby deteriorating the quality and clearness of fluorescent display. In addition, if the display-defect regions S further widen, it becomes impossible to accurately display the desired shape.
One of the conventional practices for preventing the occurrence of the above-mentioned display-defect regions S is to provide the pattern display sections at wider intervals so that an electric field formed by a grid 3 corresponding to a pattern display section 1 adjacent to that of interest may not have influence on the anodes 2 of the latter.
For instance, if the distance l.sub.1 between the left-end boundary of the anode area of the pattern display section 1b and the left-end line of the meshy portion "m" of the grid 3b is sufficiently increased, it becomes possible to prevent the occurrence of the above-mentioned display-defect regions S.
In this practice, however, the distance L between the pattern display sections 1a and 1b becomes very great, since the distance L has the following relationship: EQU L=2(l.sub.1 +l.sub.2)+l.sub.3
where l.sub.1 is defined as above or the distance between the right-end boundary of the anode area of the pattern display section 1a and the right-end line of the meshy portion "m" of the grid 3a, l.sub.2 the width of the frame portion "f" of each of the grids 3a and 3b, and l.sub.3 the space between the grids 3a and 3b. As a result, it becomes difficult to perform fine and accurate display and, in addition, to make the pattern display sections compact.